1. Field of the Invention
The present invention relates to an optical writing device. More specifically, the present invention relates to an optical writing device that is capable of writing image information to a display recording medium having a property of memory.
2. Description of the Related Art
Other than a paper medium and an electronic display device as display recording media, a display recording medium having the advantages of both the electronic display and the paper medium has recently been drawing attentions.
Such display recording medium has a property of memory for display. Thus, it is only necessary to supply energy when rewriting information, and unnecessary to supply energy for maintaining the display. Further, the display recording medium exhibits a character of low environmental load, since it is repeatedly rewritable.
As a method for writing an image to the display recording medium having such character, there is a method of writing image information through controlling voltages applied to the display recording medium by an amount of light irradiated to the display recording medium other than a method of controlling image information only through controlling the voltages by spatially arranging switching elements such as thin film transistors in matrix on the display recording medium. Japanese Unexamined Patent Publication 2001-301233 (Patent Document 1) proposes such optical writing device.
The display recording medium depicted in Patent Document 1 is in a structure in which a display layer formed with a liquid crystal having a property of memory and a photoconductive layer whose resistance value decreases in accordance with the amount of irradiated light are laminated between a set of transparent electrodes. Further, the optical writing device for the display recording medium is in a structure in which a two-dimensional micro lens array is disposed on a transmission-type liquid crystal panel to form an image by the light emitted from the liquid crystal panel on a photoconductive layer of the display recording medium by using the two-dimensional micro lens array.
When writing to the display recording medium, the resistance value of the photoconductive layer is changed by the emitted light amount distribution based on image information emitted from the optical writing device and controlling the voltage applied to the display layer so as to record the image according to the light amount distribution on the display layer.
With this type of optical writing device, the image is formed on the photoconductive layer of the display recording medium by the two-dimensional micro lens array, and the resolution of the image written to the display recording medium is increased. Thereby, the directivity of the light emitted from the optical writing device is increased.
In the meantime, separately from the method that increases the directivity of the emitted light by the image formed with the light, there is proposed a display device whose directivity of the emitted light is increased by disposing a micro louver on the display device such as a liquid crystal display. This is shown in FIG. 6A and FIG. 6B.
The display device shown in FIG. 6A is an example of the display device in which the directivity of the emitted light is increased by disposing a micro louver 101 on a display panel 100 formed with a liquid crystal display device. This display device is formed with the display panel 100 formed with a plurality of pixels arranged in matrix, and the micro louver 101 disposed on the display panel 100.
As shown in FIG. 6B, the micro louver 101 is in a structure in which a periodical structural body in which a light absorption layer 102 and a transparent layer 103 are arranged alternately is sandwiched between two protective films 104a and 104b. Period P in terms of the layout of the light absorption layer 102 and the transparent layer 103 is set to be constant.
Only the light that makes incident within a range of visible angle θ transmits through the transparent layer 103. The light outside the range of the visible angle θ is absorbed by the light absorption layer 102. The visible angle θ is determined according to thickness D of the periodic structural body and the pitch P of the period. The smaller the visible angle θ is, the more the directivity of the light transmitted through the micro louver 101 is increased.
However, as described above, both the display panel 100 and the micro louver 101 of this kind of liquid crystal display device have the periodic structure. Thus, the light transmitted through the micro louver 101 comes in a state where two regular intensity distributions based on the respective periodic structures overlap with each other, thereby generating moiré fringes according to the difference in both spatial frequencies.
For this, there is known a method for suppressing generation of the moiré fringes. Japanese Unexamined Patent Publication 2007-256330 (Patent Document 2) and Japanese Unexamined Patent Publication 2008-89727 (Patent Document 3) show such method.
In Patent Document 2, a micro louver is obliquely disposed on a display device to increase the difference between the spatial frequency stemmed from the two-dimensional periodic structure of the display device and the spatial frequency according to the period of the micro louver so as to suppress generation of the moiré fringes.
Further, in Patent Document 3, a micro louver disposed on a display device forms a two-dimensional periodic structure that includes periodic structures of different phases in x-direction and y-direction. In the directions of different phases, the in-plane distribution of the emitted light passed simultaneously through each periodic structure in the surface direction is leveled to suppress generation of the moiré fringes.
However, there are following issues with the documents of the related techniques described above.
In Patent Document 1, an image is formed on the photoconductive layer of the display recording medium by the two-dimensional micro lens array disposed on the transmission-type liquid crystal panel. Thus, there is an issue of having such a phenomenon that the image written to the display recording medium becomes blurred depending on the positioning accuracy of the two-dimensional micro lens array and the positioning accuracy of the display recording medium, i.e., an issue of deteriorating the resolution of the written image.
Further, in Patent Document 2, the micro louver is obliquely disposed on the display device to seemingly increase the difference in the spatial frequency generated stemmed from the two-dimensional periodic structure of the display device and the spatial frequency according to the period of the micro louver so as to suppress generation of the moiré fringes. However, it is insufficient. Thus, the moiré fringes are to be written to the display recording medium, thereby deteriorating the resolution and quality of the written image.
Furthermore, in Patent Document 3, generation of the moiré fringes can be suppressed in the directions of different phases by disposing the periodic structures of different phases. However, the relation between the pixel pitch of the display device and the pitch of the micro louver is unknown, so that the numbers of light absorption layers of the micro louver existing within the pixels of the display device become nonuniform within the substrate surface. As a result, variations are generated in the transmittance of each pixel.
For example, in a case where a micro louver with the light absorption layer in width of 10 μm and the period pitch of 50 μm is applied to a display device with the pixel pitch of 160 μm, there are a case of having two light absorption layers and a case of three light absorption layers within a single pixel. Thus, there may sometimes generate unevenness in the distribution of the light amount emitted from the optical writing device, which deteriorates the quality of the image written to the display recording medium.
It is therefore an exemplary object of the present invention to provide an optical writing device that is capable of effectively suppressing deterioration in the resolution and deterioration in the quality of the images written to the display recording medium.